Two-way telephone system



Apr 8, 933 s. B. WRIGHT El Al.

TWO-WAY TELEPHONE SYSTEM Filed June 13, 1931 Doule Drmmal Eclw Juppressam Circuit 2 Circuit INVENTORS 61B W ATTORNEY Patented Apr. 18, 1933 TED STATES PATENT A QFFICE:

SUMNER IB. WRIGHT, OF SOUTH ORANGE, v.ANI) DOREN MITCHELL, 0F MABTINSVILLE, NEW JERSEY, ASSIGNQRS TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY,

A CORPORATION oE'NEw Yon'i:

'rwo wAY TELEPHONE SYSTEM Application filed June 13,

. This invention relates to two-way systems for the transmission'of-energy between distant stations for the production of some desired over-all effect. 7 More particularly, the

invention relates to two-way telephone systems having one or more comparatively unstable links and equipped with Wave responsive devicessuch as singing suppressors for controlling the transmission over the voice channels. With greater particularity, the invention relates to methods of transmission control which permit the use in tandem of two or more telephone'circuits of which at least one is noisy or unstable.

In a long telephone system it is often desirable in order to prevent.singing to have one or both of the one-way paths normally dis-' abled at one or more points. It follows that means must be provided whereby the voice waves will cause the removal of any'such disability normally found on the path over which these waves are to be transmitted.

It may be that two'long four-wire circuits,

for instance, "are so located that it is convenient to connect them in tandem for extended transmission. One of these circuits, however, may include what will be hereinafter termed a mutable linkthat is, a link capable of or liable to change (from internal'or external cause) which may give rise to interfering energy, or, more specifically, alink specially subject to noise, fading (in the case of radio transmission) or change of impedance. If transmission is effected from the mutable cir- 'cuit to the other circuit, wave responsive de- .fading effects are likely to be present, and in the case of a wire circuit changes of temperature, for instance, may produce the objection able mutability. r g r If two circuits are to be connected in tandem as suggested above, a possible remedy is the removal of the transmission control devices at the circuit terminals which are connected together. This possible remedy, however, is open to several objections. ;In the case of radio circuits there is often con- 1931. Serial No. 544194.

siderable transmission from a transmitter to the local receiver, and 1n order toprevent the undesirable effects of this radio coupling,

, ratus to render satisfactory the transmission over two or more four-wire c1rcu1ts of the type indicated above when the circuits are operated in tandem. In general, the applicants accomplish their object by using control energy which is applied at the transmitting end of the mutable circuit in response to voice'waves and is made to operate the singing suppressor apparatus at the receiving end of the circuit. Thecontrol Wave, inaddition to being confined to a narrow frequency bandand thus easy to detect inspite of interfering noise, is applied suddenly with full amplitude and thus has the further advantage over speech waves of producing a prompt and positive operation 7 v of the transmission controlling relays.

It will be understood that while it is desirable to make certain somewhat specific disclosures of the application of the invention,

the applicants methods are applicable to a great variety of long transmission systems.

For instance, the mutable link may be a radio link or a submarine cable; Again, the connected circuits may be composed of various transmission media and may be equipped with various types of wave responsive devices for transmission control.

It is proposed to describe the invention in connection with a limited number of long two-way telephone systems, and accordingly the following description should be read with reference to the accompanying drawing.

Figurel of the drawing shows schematically two four-wire circuits connected in tandem and indicates the application of the applicants transmission control. Fig. 2 shows diagrammatically and in part schematical- 1y, :1 part of a system such as that disclosed schematically in Fig. 1 and shows in somewhat greater detail the arrangement of the transmission control apparatus. Fig. 3 of the drawing shows schematically the application of the invention to a long two-way system comprisingthree four-wire circuits of which the middle circuit is mutable. Like reference characters in the several figures of the drawing designate corresponding parts, particularly in the case of Figs. 1 and 2.

With reference first to Fig. l, the scheme indicates two four-wire circuits, one extending from station WV to station W and the other extending from station E to station E. The first circuit may be extended to the left through a connecting circuit L, and the second four-wire circuit may be extended to the right through circuit L. It will be understood that the heavy lines each represent a two-wire transmission path and that the connections between the four-wire circuits and the circuits L and L, which are twowire circuits, may be effected in any suitable manner. It is to be understood further that stations W and E may be very close together or may be the same station. The point to be understood is that these two fourwire circuits are to be connected in tandem at some point X which may lie between stations W and E or may be the common point of the two stations.

It is believed that the conventional disclosure employed in connection with the scheme of Fig. 1 and the nature of the apparatus schematically indicated will be clearly understood from the following description and discussion.

In the case of transmission from the twowire circuit L at the left to the two-wire circuit L at the right, the transmission is effected over the one-way path L L extending from station W to station W and the one-way path L L extending from station E to station E. The path L,L is normally disabled at points 7) and h. and the indicated intervening link is understood to be mutable, by reason, for instance, of being a radio link. Likewise the path L L is normally disabled at points is and c, and again it is understood that the intermediate link indicated by the broken lines is a mutable link such as a radio link.

According to the applicants invention, when voice waves travel from the line L over the path L they pass through a volume control device to the point a. At this point a portion of the transmitted energy is diverted to operate wave responsive apparatus such as an amplifier-detector having connected in its output relays which control contacts associated with the transmission paths. Through the operation of such means the energy diverted at point a renders the path L operative at the normally disabled point 6 and applies to the path L control energy from the source indicated, which energy may take the form of alternating current waves of frequency f,. In addition, the energy diverted at point a disables the opposite oneway transmission path L at point 0. It will be understood from the discussion contained hereinbelow that in response to energy passing in the opposite direction a certain operation may be effected at the point f which will prevent the above described effects of the energy diverted at point a.

This control energy now travels over the path L the voice waves being preferably somewhat delayed in a manner well understood in the art. When the control energy reaches station W a portion is diverted at point 9 to operate apparatus similar to that suggested at station W to render the path L operative at the point of normal disability 72.. In addition the control energy breaks an auxiliary circuit at point 11, thereby preventing the effects which would otherwise be produced by energy traveling in the opposite path L and diverted at point j. It will be understood that the particular transmission control system discussed is based on the following arrangement: If the waves in path L2 pass the point Z before the waves in the opposite path L reach the point 7', transmission from left to right in path L is assured. whereas, if the energy in path L arrives first, the path L is disabled at point Z and the transmission control apparatus associated with that path is temporarily disabled.

The filter F passes only the control energy from the source f whi e the filter F passes only the voice waves. Thus the transmission control operation at point it is effected only in response to the control energy. and the control waves. having performed their function at station WV. are excluded from the transmission path L It will be noted that the two four-wire circuits are connected directlv in tandem at point X; that is. the paths L and L adapted for transmission in the same direction are connected together, and the paths L and L3 adapted for transmission in the opposite direction are connected directlv together. It is to be understood that this direct four-wire connection is not essential to the application of the invention. The connection may be made on a two-wire basis. It will be understood further, however. that it is the applicati on of the invention which permits the direct four-wire connection and that if the connection is made on a two-wire basis the twowire balance becomes unimportant.

The voice waves traveling from circuit L tocircuit L next pass through the volume control devices at point X, and at that section of the system designated as station E a portion of the voice energy isdiverted at:

point j to perform a'function which is the same as that discussed in connection with stae tion W. If no disability has been applied at point z", the path L is rendered operative at the point of normal disability control Waves of frequency f are applied from the source indicated and an auxiliary disabling operation is performed at point Z on path L The control energy passes over the in-' termediate link, which may be mutable, this control energy somewhat preceding the voice energy, and passes the point 0 at station E. If no disability has been applied at that point in response to voice waves in the opposite path L at point a, a portion of the controlenergy isdiverted, passes through filter F renders the path L operative at point e and disables an auxiliary circuit at f to prevent transmission control operations in response With the paths L L L and L correspond to the apparatus associated with the left to right channel and are correspondingly designated by reference characters. At station E in-response to voice waves from circuit L a controlfrequency fris applied to the path L and'is transmitted to the path Y L at station E, where it eifectstransmission control as described above. Likewise at station W a control frequency f is applied. a to the path L is transmitted'over the path L at station W and there performs the transmission controlling function. p

From the above description and discussion it will be understood that'in connection with transmission from left to right false operation of the transmission control apparatus at station E and E by noise energy originating in the mutable link between stations W and W is prevented since the singing suppressor of station W is operated only when voice waves travel over the path L at station W and apply the control energy. Likewise it'- will be understood that the transmission 'control apparatus associated with the right to left transmission path at stations W and W cannot be operated by noise energy originating between stations E and E since the control at point h is the function of the control frequency f, appliedat station E only in re sponse to the voice waves. It should be noted further in connection with transmission from 7 left to right, for instance, that noise origi- 1 nating in the mutable link-between stations E; and E cannot be transmitted onto circuit 7 L, except when. speech is also present, since the transmission at point e is under the control of the control energy applied at station E. Likewise noise originating in the mutable link betweenstations W and W cannot pass on to the circuit L over the path L in the absence of the operation at point e, which is performed only by the control frequency f applied in response to voice waves traveling from right to left. In short, the applicants invention prevents the passage of noise energy from a mutable circuit to a connected circuit except when voice waves are traveling over the clrcuit; accordingly, only the desired operation of transmission control apparatus is permitted' 7 In Fig. 2 it is assumed that the unstable link to the left of station W and the unstable link to the right of station E. are radio links. Thus, the transmission path L is that Whichnormally leads from a radio re-' ceiver to some terminal point at X,and the pathL is one which normally leads from a terminal point to the radio transmitter from which waves are sent out to the right over'aradio link. Theconnection of the two circuits at point X is shown in full line as a four-wire connection. It will be noted,

I however, that there are disclosed aconnect in'g two-wire line LL, hybrid coils H and H and balancing networks N and N, and the.

broken line connections indicate that the two four-wire circuits may be connected together over this apparatus. In this case it will be understood that the balances between the line LL and the networks N and N are relatively i unimportant.

Furthermore, under I certain conditions, the hybrid coilsand balancing networks may be omitted.

:The transmisslon control apparatus scheniatically indicated in 1 at stations W and E is diagrammatically disclosed in Fig.

2 and will now be discussed with some additional detail.

The control energy picked up by the. antenna at stationW passes through the radio receiver and over the line L to point g. A

portion of this energy is diverted and passes through the filter F which excludes substantially different frequencies. The amplifier-detector AD operates in response to the control energy, and relays B and-R connectedin the output circuit of the amplifierdetector are operated. Relay R removes the. disability from the path L at point h, and

relay R breaks the output circuit of the amplifier-detector AD associated at point with the opposite path L It will be underv stoodthat if energy flowing in the opposite direction arrives before the energy in path L the amplifier-detector AD operates re- =taken by the waves in the opposite path L,.

It being assumed, however, that the control energy in path L has rendered that path operative at point 72,, the voice waves are permitted to pass on through the volume control ;device to the point X. As stated above, in

connection with Fig. 1, however, transmission of the control energy is prevented by filter F which passes only the voice frequencies. At station E a portion of the voice energy is diverted at point 7' to operate the amplifier-detector AD The relay R now operates unless control has been taken by voice waves in the opposite direction, and the path L is rendered operative at the point of normal disability is. The operation of relay R also permits the control current of frequency f from the oscillator to pass through the filter F and through the radio transmitter for transmission from station E. The delay circuit shown between point j and k serves to delay the voice waves and permit the control energy to precede the voice energy. The filter F serves to eliminate transients set up by the application to the transmission path of the oscillator.

The transmission from right to left in the circuits of Fig. 2 is similar to the transmission from left to right just described. A portion of the control energy received at station E is diverted at point 9', passes through the filter F and operates amplifier-detector AD unless-control has been taken by waves passing in the opposite direction. Relays R and R will operate. Relay R renders the path L operative at point h, and relay R opens a contact at oint i to disable the output of the ampli er-detector AD, including the relay R The voice waves pass through filter F which excludes the control current.

At station W the voice waves in path L reach the point j, where a portion of the energy is diverted to operate amplifier-detector AD If the output circuit of this amplifier-detector has not been disabled at point i in response to energy in the opposite path L relay R operates. This relay operation clears the path L, at point is, disables the output circuit of amplifier-detector AD and applies the control frequency f from the oscillator to the path L The filter F serves to eliminate transients.

The detailed description given above in connection with Fig. 2 of the drawing will serve to clarify the arrangement and operation of the circuit of Fig. 1 and to make clear the application of the applicants invention to two long four-wire circuits connected in tandem.

In Fig. 3 there is disclosed a long twoway system including three four-wire circuits 1, 2 and 3, connected in tandem. Circuit 1, which may be understood to be a comparatively stable circuit, is equipped with simple echo suppressor apparatus. Circuit 3, likewise stable, is equipped at each end with double terminal echo suppressor apparatus.

Circuit 2 is understood to include a mutable link, which may be a radio link or any link rendered mutable in one of the ways suggested hereinabove.

In connection with transmission from left to right, the applicants cause the voice waves at the transmitting end of circuit 2 to send a control current of frequency f, to the right end of circuit 2. This control energy passes through filter F and functions as described above. Filter F 3 passes the voice energy but excludes the control energy. This arrangement serves to prevent operation of the echo suppressors of circuit 3 except in response to the voice waves. In other words, noise energy or the like from the mutable link of circuit 2 cannot reach circuit 3 to cause false operation of the echo suppressors when no voice energy is being transmitted.

In connection with transmission from right to left, voice energy reaching circuit 2 sends out the control frequency f from the transmitting end to the receiving end of the 1 circuit, Where this control energy passes through filter F and performs its transmission controlling function. The filter F passes the voice waves but excludes the control current. Accordingly, the echo suppressor of circuit 1 is rendered exempt from false operation from noise energy or the like arising in circuit 2.

While the applicants methods of and ar rangements for transmission control have been disclosed in connection with a limited number of transmission systems, it will be understood that the invention is applicable to many other transmission systems involving different transmission media and different types of wave responsive auxiliary apparatus for controlling transmission over component sections of either one way channel, within the scope of the appended claims.

What is claimed is:

1. In a system for the transmission of energy, including a mutable transmission path and other transmission paths connected in tandem therewith, the method of controlling transmission over the system which consists in causing the energy transmitted there over for the production of the desired overall elfectto apply control energy to the transmitting end of the mutable path, causing the control energy to control the transmission over the receiving end of said path, and excluding the control energy so applied from forms the above-stated connected in tandem therewith, means near the receiving end of the first path responsive to energy therein for controlling the transmission thereover and means associated with the secondipath and responsive to energy therein for controlling the transmission thereover, the method of preventing falsev operation of the controlling means associated with the second path by interfering energy originating in the first path which conslsts in causing the energy transmitted for the production of the desired over-all effect to apply control energy to the transmitting end of the first-path, causingthe controlling means near the receiving end of the first path to respond only to said control energy, and excluding the control energy from the system before it is transmitted on to the second path. 1

3. In a system for the transmission of energy, a transmission link which is mutable, other transmission links adapted to be connected'in tandem therewith, means at the transmitting end of saidmutable link responsive to the energy transmitted to produce the desired over-all effect for applying control energy thereto, means at the receiving end of said mutable link responsive substantially only to the control energy for controlling the transmission thereover, and means at said receiving end for excluding the control energy from the transmission channel.

4. In a system for the transmission of energy, including a mutable transmission link and a second transmission link positioned so as to be available for transmission from said mutable link but including transmission control means which will not normally operate satisfactorily when said second link is connected to said mutable link, the method of rendering the transmission satisfactory which consists in causing the energy transmitted for the production of the desired over-all effect to apply control energy to the transmitting end of said mutable link, and

which consists in causing the energy trans mitted for the production of the desired over- -all effect to apply control energy to the transmitting end of said mutable link, causing the control energy to control the transmission over the receiving end of said mutable link, and excluding the control energy from the system before it is transmitted on to said second link.

. 6. In a two-way system for the transmission of energy, including twofour-wire ciricults connected in tandem and providing two extended one-way paths adapted for transmission in opposite directions, and means near each end of each four-w1re c1rcu1t'respon-' sive to energy in the local section of one of the one-way paths for controlling the trans.- mission thereover, the method of transmission control of the tandem circuit which consists in causing the energy transmitted for the production of the desired over-all effect, as it travels over the transmitting path at either end of either four-wire circuit, to apply control energy thereto, and causing the transmission controlling means at the distant end' of that four-wire circuit to respond substantially only to said control energy.

7. In a two-way system for the transmission of energy, including two four-wire circuits connected in tandem and providing two extended one-way paths adapted'for transmission in opposite directions, and means near each end of each four-wire circult responsive to energy 1n the local section --of.one of the one-way paths for controlling the transmission thereover, the method of 7 transmission control of the tandem circuit -which consists in causing the energy transmitted for the production of. the desired over-all effect, as it travels over the transmitting path at either end ofceither four- -wire circuit, to apply control energy thereto, causing the transmission controlling means at the distant end of that four-wire circuit to respond substantially only to said control energy, and eliminating the control energy at said distant end of the four-wire circuit. when said links are connected in tandem 8. In a two-Way system for the transmission of electrlcal waves, comprlslng two twoway circuits each havlng separate paths adapted for transmission in opposite directions and each having wave responsive apparatus for controlling the transmission Over the transmission paths, the method of transmitting electrical waves over said circuits without subjecting the Wave responsive apparatus of one circuit to false operation by noise mitted for the production of the desired overall effect, as they travel over the transmitting .end of each of the paths of said circuits, to re .move the disability from said end and to send out control waves, causing said control waves ratus for controlling the transmission over to remove the disability from the receiving end of said path and to maintain the operative condition thereof during the arrival of the waves transmitted for the production of the desired over-all effect, and connecting directly together the paths of the two circuits adapted for transmission in the same direction.

9. In a two-way system for the transmission of electrical waves, comprising two two- Way circuits each having separate paths adapted for transmission in opposite directions and each having wave responsive apparatus for controlling the transmission over the transmission paths, the method of transmitting electrical waves over said circuits without subjecting the Wave responsive appara-tus of one circuit to false operation by noise waves originating in the other circuit, which consists in causing the one-way paths of both circuits to be normally disabled near their respective terminals, causing the waves transmitted for the production of the desired overall eifect, as they travel over the transmitting end of each of the paths of said circuits, to remove the disability from said end and to send out control waves, causing said control waves to remove the disability from the receiving end of said path, excluding the control waves from further transmission, and connecting directly together the paths of the two circuits adapted for transmission in the same direction.

10. In a two-way system for the transmission of electrical waves, comprising two twoway circuits each having separate paths adapted for transmission in opposite directions and each having wave responsive apparatus for controlling the transmission over the transmission paths, the method of operating said circuits in tandem which consists in causing each one-way path to be normally disabled near each of its terminals, causing the waves transmitted for the production of the desired over-all effect, as they travel over the transmitting end of each of said paths, to remove the disability from said end and to send out control waves, causing said control waves to remove the disability from the receiving end of said path and to maintain the operative condition thereof during the arrival of the waves transmitted for the production of the desired over-all effect, and providing for the direct transmission between a path of the one two-way circuit and the path of the other two-way circuit adapted for transmission in the same direction of the waves transmitted for the production of the desired over-all effect.

11. In a two-way system for the transmission of electrical waves, comprising two two-way circuits each having separate paths adapted for transmission in opposite directlons and each having wave responsive appathe transmission paths, the method of operating said circuits in tandem which consists in causing each one-Way path to be normally disabled near each of its terminals, causing the waves transmitted for the production of the desired over-all effect, as they travel over the transmitting end of each of said paths, to remove the disability from said end and to send out control waves, causing' said control waves to remove the disability from the receiving end of said path, eX- cluding the control Waves from further transmission, and providing for the direct transmission between a path of the one two-Way circuit and the path of the other two-way circuit adapted for transmission in the same direction of the waves transmitted for the production of the desired over-all effect.

In testimony whereof, We have signed our names to this specification this 12th day of June 1931.

SUMNER B. WRIGHT. DOREN MITCHELL. 

